Various processes for producing aldehyde and/or alcohol compounds by the reaction of a compound having at least one olefinic carbon-to-carbon bond with carbon monoxide and hydrogen in the presence of a catalyst are known. Typically, these reactions are performed at elevated temperatures and pressures. The aldehyde and alcohol compounds that are produced generally correspond to compounds obtained by the addition of a carbonyl or carbinol group, respectively, to an olefinically unsaturated carbon atom in the starting material with simultaneous saturation of the olefin bond. Isomerization of the olefin bond may take place to varying degrees under certain conditions. Thus, as a consequence of this isomerization, a variety of products may be obtained. These processes are typically known as hydroformylation reactions and involve reactions which may be shown in the general case by the following equation:

In the above equation, each group R1 to R4 may independently represent an organic radical, for example a hydrocarbyl group, or a suitable atom such as a hydrogen or halogen atom, or a hydroxyl group. The above reaction may also be applied to a cycloaliphatic ring having an olefinic linkage, for example cyclohexene.
The catalyst employed in a hydroformylation reaction typically comprises a transition metal, such as cobalt, rhodium or ruthenium, in complex combination with carbon monoxide and ligand(s) such as an organophosphine. Representative of the earlier hydroformylation methods which use transition metal catalysts having organophosphine ligands are described in U.S. Pat. No. 3,420,898, U.S. Pat. No. 3,501,515, U.S. Pat. No. 3,448,157, U.S. Pat. No. 3,440,291, U.S. Pat. No. 3,369,050 and U.S. Pat. No. 3,448,158.
In attempts to improve the efficiency of a hydroformylation process, attention has typically focussed on developing novel catalysts and novel processes for recovering and re-using the catalyst. In particular, novel catalysts have been developed which may exhibit improved stability at the required high reaction temperatures. Catalysts have also been developed which may permit the single-stage production of alcohols rather than a two-step procedure involving separate hydrogenation of the intermediate aldehyde. Moreover, homogeneous catalysts have been developed which may permit improved reaction rates whilst providing acceptable yields of the desired products.
Although organophosphine modified cobalt catalysts are known to be excellent catalysts in a single step hydroformylation reaction of olefinic compounds to alcohols, the use of such catalysts can also lead to the production of paraffins as a by-product. These paraffin by-products have very little commercial value. It would therefore be desirable to reduce the amount of paraffin by-products formed in the hydroformylation process using organophosphine modified cobalt catalysts.
Furthermore, we have detected that cobalt catalysts comprising cobalt in complex combination with carbon monoxide and an organophosphine ligand may decompose during the reaction to produce solid cobalt deposits such as cobalt and cobalt carbide (a compound of cobalt and carbon, empirical formula CoyC, where y is in the range of from 2 to 3). Cobalt carbide is catalytically inactive in hydroformylation reactions. The presence of cobalt carbide also promotes further degradation of the cobalt catalyst, thereby resulting in an increased rate of catalyst usage. The cobalt carbide is not only catalytically inactive in hydroformylation reactions but also has a relatively bulky, porous structure and is insoluble in the reaction medium. This represents a significant disadvantage, particularly for homogeneous cobalt catalysts, because the cobalt carbide typically tends to agglomerate and form detrimental deposits on the internal surfaces of the production facility. The deposition of cobalt carbide impedes the running of a hydroformylation production facility with optimal efficiency. In particular, the deposition of cobalt carbide can cause plugging of the pipe work in the production facility, resulting in shut down of the production facility to allow for removal of these cobalt carbide deposits.
The present invention therefore seeks to provide a simple hydroformylation process which may be used in the single step conversion of olefinic compounds to alcohols, which not only reduces the amount of paraffin by-products produced, but also reduces the amount of cobalt catalyst lost through decomposition and formation of cobalt carbide and/or cobalt deposits on the internal surfaces of the production facility.
Additionally, since the demand for normal 1-alcohol products is greater than the demand for other alcohol products, it would also therefore be desirable to increase the proportion of normal 1-alcohols in the alcohol product composition.
U.S. Pat. No. 6,482,992 describes a process for the hydroformylation of olefins to give alcohols and/or aldehydes in a plurality of hydroformylation stages, each of which comprises: a) hydroformylating olefins having a carbon atom content of 6 to 24 carbon atoms in the presence of a cobalt- or rhodium catalyst in a reactor to the point of conversion of olefin reactant to product of 20 to 98%; b) removing the catalyst from the resulting liquid discharged from the reactor; c) separating the resulting liquid hydroformylation mixture into a low-boiler fraction comprising olefins and paraffins, and a bottoms fraction comprising aldehydes and/or alcohols; and d) reacting the olefins present in the low-boiler fraction in subsequent process stages comprising steps a, b and c and combining the bottoms fractions of process steps c) of all process stages. Different reaction conditions can be set in the hydroformylation reactors.
U.S. Pat. No. 5,112,519 describes a process for hydroformylation of olefins having the formula (C3)x, (C4)x or mixtures thereof, where x has the value of 1 to 10, using a catalyst with a phosphine ligand at a temperature sufficient to promote reaction while retarding paraffin formation. A hydroformylation process disclosed in U.S. Pat. No. 5,112,519 is conducted in a single reactor, wherein the hydroformylation temperature is held at 135° C. for 2 hours, followed by a reaction temperature of 160° C. for 48 hours (Example 2). The reason for the use of the initially lower temperature is stated as isomerising the double bond of the olefins to the chain end.